The invention relates to a multistage piston compressor comprising a valve casing and a shiftable valve piston formed as a single piece and driven linearly oscillating by a drive motor, wherein the multistage piston compressor is furnished with at least one volume changeable low-pressure chamber with an intake check valve and with at least one volume changeable high-pressure chamber with a discharge check valve, wherein the valve piston includes a low-pressure piston and a high-pressure piston and wherein the low-pressure chamber and the high-pressure chamber are connected to each other through an overflow duct, wherein an overflow check valve opening in the direction toward the high-pressure chamber is inserted in the overflow duct.
Such piston compressors are employed in all technical fields, where there exists a need for compressed air. Primarily such piston compressors are applied in the vehicle industry for pneumatic suspension and/or air damping.
Such a piston compressor in a two-stage construction is for example described in the German printed Patent document DE 197 15 291 A1. This piston compressor comprises a compressor casing, where a cylindrical low-pressure chamber with a larger low-pressure piston and a cylindrical high-pressure chamber with the smaller high-pressure piston are formed in the compressor casing. Here the low-pressure chamber and the high-pressure chamber are disposed on a common axis and the low-pressure piston and the high-pressure piston are formed to a single piece pressure piston with a common piston rod. The low-pressure chamber is furnished with an intake with an intake check valve, the high-pressure chamber is furnished with an outlet with a discharge check valve and the two pressure chambers are connected by an overflow channel, wherein an overflow check valve is disposed in the overflow channel. A crank pin of a crankshaft engages with the common piston rod of the low-pressure piston and of the high-pressure piston at a right angle alignment, wherein the crankshaft is driven for example by an electric motor and wherein the crankshaft transforms the rotary motion of the crankshaft into a linear motion at the single piece pressure piston. An oscillating motion results at the pressure piston from this linear motion.
The intake check valve, the discharge check valve, and the overflow check valve have sealing discs made of spring steel, wherein the sealing discs of the spring steel are attached by a middle screw as is the case with the intake check valve and with the overflow check valve and wherein the sealing discs of spring steel cover in a sealing way several flow channels disposed on a partial circle, or which sealing discs are held by a sideways staggered screw as is the case with the discharge check valve and which sealing discs seal off a next disposed flow channel.
These check valves perform their object only in an insufficient way. It is to be noted that the metallic sealing discs do not seal sufficiently. This can be traced to the fact that the closure and sealing force of the sealing discs is furnished exclusively by the proper tension of the spring steel. Frequently, a tensioning force acts opposite to the closure and sealing force, wherein the tensioning force starts from the attachment screw and prevents a smooth resting of the sealing disc in a pressure balanced state. Leaks occur also by the fact that fatigue situations occur at the sealing disc in the course of time and that the sealing discs to not rest perfectly at the sealing surface for this reason. The sealing discs are usually furnished stronger for balancing these disadvantageous effects. This in turn increases again the incorporation space of such a sealing disc and decreases the volume of the corresponding pressure chamber. Such piston compressor's are then not very powerful. The higher closure force obtained by reinforcing the sealing disc simultaneously increases however the required opening force for the free flow through, which opening force has to be furnished by the system pressure. This also decreases substantially the degree of effectiveness of the piston compressor. It has also become apparent that the material of the sealing discs fairly quickly fatigues because of the high frequencies of the piston compressor and therefore only a small lifetime of the sealing discs can be recorded.
Finally, the production of the sealing discs out of spring steel is very involved, since on the one hand the material is hard to work with and on the other hand high requirements are placed on the quality of the sealing face at the sealing disc.
Therefore it is an object of the present Invention to develop a piston compressor of the recited kind, wherein the check valves exhibit a low closure force and at the same time assure a high sealing effectiveness.